Compensation for variations in phase change



Dec. 24, 1940. 1 N 2,225,653

COMPENSATION FOR VARIATIONS IN PHASE CHANGE Original Filed Feb. 21, 1939 2 Sheets-Sheet 1 I m I g I I A B FIG 4 7" n Z 200 JNGLE METER INVENTOR 1 N MON/f Br Dec. 24, 1940.

N. MONK COMPENSATION FOR VARIATIONS IN PHASE CHANGE Original Filed Feb. 21, 1959 POWER SYSTEM A AIAA POWER SYSTEM 8 PHASE ANGLE METER Plus: 300- COMPENSATOH A l PILOT CIRCUIT b Pawn .rrsrsu '4 FIG. 7

v I PILOIffCll/T PHI SE COHPENSA TOR 2 Sheets-Sheet? 500M nai /0.9mm.

APPA 04 7'04 IN l/E NTOR MMONK BY 4 AZTORNEV Patented Dec. 24, 1940 UNITED I STATES PATENT OFFICE.

COMPENSATION FOR VARIATIONS IN PHASE CHANGE Newton Monk, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New. York, N. Y., a corporation of New York Original application February 21, 1939, Serial No.

257,674. Divided and this application December 20, 1939, Serial No. 310,129

6 Claims. (Cl. 172-246) characteristic of a transmission circuit particu-' larly' at any one frequency and is applicable more especially to a cable circuit.

An object of this invention is to provide a new and improved method and means for substantially reducing variations in the phase characteristics of a cable circuit particularly at any one frequency due to varying weather conditions or other causes. Another object is to provide a method and means for improving transmission characteristics of cable circuits.

A further object is to provide a pilot circuit, in which variations in phase change are substantially eliminated, for use in measuring the phase relationship of the current at different points in an electrical system.

This is accomplished primarily by terminating each end of the circuit in a specific impedance as described below. The method is applicable to those circuits for which the shunt impedance of the equivalent T-network remains very nearly a pure reactance for various conditions to which a cable may be subjected, such, for example, as temperature changes; in other words, for cases in which the eii'ect of leakage is very small or negligible. This is true for transmission of currents of frequencies up to the order of several thousand cycles over cable circuits of some length.

A description of an embodiment chosen for illustrating this invention, in which reference is made to the accompanying drawings, follows:

Fig. 1 is an equivalent T-network of a cable circuit;

Fig. 2 is an equivalent T-network ofthe cable circuit of Fig. 1 showing the impedance changed due to varying weather conditions or the like;

Fig. 3 shows an application of terminating impedances according to the principles of this invention for compensating for variation in phase characteristic of a circuit when an alternating current is transmitted thereover;

Fig. 4 shows an application of this invention.

for measuring by means of a pilot line the phase differences between voltages at. two points;

Figs. 4A and 4B show different arrangements for connecting an alternating voltage source to the pilot line arrangement of Fig. 4; Fig. 5 shows an application of this invention t e 0 cur ents is zero.

for measuring by means of a pilot line the phase differences between voltages at two points in which compensation is introduced for the change in phase introduced by the pilot line itself; I Fig. 6 shows an application of this invention 5 formeasuring by means of a pilot circuit the phase angle diiferences between different points of a power system or systems; and

Fig. 7 shows an application of this invention to power transmission for automatically maintain- 10 mg the current at different points of the system or systems in phase.

The underlying principles of this invention are first described by referring to the equivalent T- network included in Figs. 1 and 2; while certain 15' applications are described in connection with subsequent figures.- i

Referring to Figs. 1 and 2, the former shows a cable circuit reduced to its equivalent T-network under given conditions, and the latter under 20 somewhat different conditions when. the impedance is changed from that shown in the former. The network is assumed to be connected to a generator E of impedance Zr and terminated in animpedance also of value Z'r. ances of the equivalent T'-network of Fig. 1 i change due to varying weather or other conditions, a new network as indicated in Fig. 2 results, in which the impedances Z1 and Z: may be considered to have new values Z1 and Z2. It the 30' leakage can be neglected the value of the shunt impedance Zz" will be equal to that of the original network or Z2.

The ratio between the currents i2 and i2 determine the variation in phase change. These 35 currents may be expressed as follows:

2 "MZ2 I) i+ T) 2+ (ZI+ZT)2 I EZ2' 2 0 2 1+ r) a+ 1+ 1) impedanoes Z1 and -Z1' (which will be only slightly different from Z1) may be neglected and the right-hand side of Equation 4 reduces to unity indicating that the phase change between If the imped- 25' It is obvious from Equation 4 that the value 2r may be any value large in comparison with Z1 and may be either a resistance or a reactance. However, it must not be so Ereat that the attenuation becomes excessive. In order to determine the best value for the impedance Zr the expression for the attenuation, that is, the relation between the currents ii and i: may be written:

LLTL, i i+ 2+ T which neglecting Z1 reduces to it Z; a ZZ+ZT (6) From this expression and the maximum value of attenuation, which may be allowed, the value for Zr may be determined.

The results which may be obtained with this method for reducing the variations in phase change of the circuit will, of course, depend upon the relative values of Z1 and Zr. If the attenuation is permitted to be large, the value of Zr can be made very large and the variation in the phase change can be eliminated for all practical purposes.

This method is applied in the following example to an actual cable circuit at 60 cycles taking a non-loaded l9-gauge cablecircuit 10 miles -in length. The fundamental constants for such a circuit at 68 F. are as follows:

R=85 ohms per mile L=.00106 henry per mile c=.066 mfd. per mile G=.1 micromho per mile It is assumed that the leakage G is equal to 0.1 micromho per mile and that it changes 50 per cent over the temperature range from 68 F. to 32 F.

Employing these fundamental constants, the equivalent T-networks for a -mile circuit work out to have the following impedance values:

If an attenuation of decibels is permitted the maximum value of resistance or reactance which may be employed for Zr is from Equation 5 about 40,000 ohms.

Substituting the above values for Z1, Z1, Z2, Z2 and Zr into Equation 3 we find that the variation in phase change-will be as follows:

Variation Z in phase change Ohms Degrees aaaaeae This compares with a total variation in phase change of about 1.0 degree which would obtain it the circuit were terminated in characteristic impedance.

The leakage in such a circuit may, however, be considerably different from 0.1 micromho per mile at 68 F. Furthermore, the change in leakage over the temperature range assumed may be considerably less than 50 per cent. If either the leakage is less than that assumed or the change in leakage is less than 50 per cent, the variation in the phase change will be .less than the computed values given above.

The figures given are merely for illustrative purposes. By increasing the value of Zr the variation in phase change can be still further reduced. This will, however, increase the overall attenuation of the circuit.

Fig. 3 shows an application of terminating impedances to a transmission line according to the principles of this invention for compensating for variations in the phase characteristics of a circuit when an alternating current is transmitted. The values of the impedances Zr at each end of the line are so determined that when the voltage of an alternating current of a given frequency generated by source E is impressed upon the line, the variation in phase change caused by the transmission line is neutralized or reduced. Such a compensated line may be used by itself or as a pilot circuit in conjunction with other circuits or systems, examples of which are subsequently described herein.

The method and means described above of providing a circuit of substantially constant phase characteristic may be utilized in various ways, a number of illustrative applications of this invention being described below.

Fig. 4 shows an application of this invention for comparing by means of a pilot circuit, such as a telephone line, the phase angle between two voltages V1 and V2 originating at different sources or stations A and B. The voltage V1 is transmitted from station A over the pilot line I00 to station B at the distant end of the pilot line where another voltage V: is to be compared with the voltage V1 by means oi a phase angle meter 200, to determine the difference in phase between the two voltages V1 and V2. The voltage V1 generated at station A is impressed upon the pilot line I00 and transmitted to the distant end at station B where the voltage is taken of! from the pilot line through series resistances R1 and R: which must have a high resistance in comparison with the impedance of the line and of the terminating impedances Zr. In order that the phase angle between the voltages V1 and V1 may be obtained from the readings of the phase angle meter 200, it is, of course, necessary to correct for any change in phase of voltage V1 which may be introduced by the line I00. This may be accomplished by measuring the phase change caused by the line itself between proper impedances Zr at each end of the line. This phase change caused by the line must then be subtracted irom the indication given by the phase angle meter in order to obtain the true phase difference between the voltages Vi and V2. The phase change caused by the line itself may be measured by any of the well-known methods, for example, that shown in W. P. Mason Patent 1,684,403, issued September 28, 1928. The phase change caused by the line itself will change with weather variations and the like and this may be minimized in accordance with this invention by terminating the ends of the line with similar impedances Z'r. the value of which may be calculated as explained above, particularly in describing Figs. 1 and 2.

Figs. 4A and 4B show alternative arrangements for connecting the source of alternating voltage to the line circuit I00. In Fig. 4A the coupling is a transformer so designed that the impedance ZT looking into the line side of the transformer is of the proper value for terminating this end of the line for effecting the desired reduction of phase variations therein. In Fig. 4B the coupling is also a transformer and, in addition, separate impedances are inserted in the line to build up the impedance Z'r looking into the line side thereof to afford the proper impedance.

Fig. 5 also shows an application of this invention for comparing by means of a pilot/line, the phase angle between two voltages V1 and V2, at stations A and B, respectively, in a manner similar to that described in Fig. 4 but without the necessity of separately measuring the phase change caused by the line itself, since in this arrangement a phase compensator 300 is employed to compensate for phase changes in the line. The action of the phase compensator 300 is such that the phase angle meter 200 is held at zero indication when the voltages V1 and V: are in phase. The phase compensator may consist of a network composed of one or more of the following elements, resistances, inductances, and capacitances. The design of such networks is well known in the art. See, for example, H. Nyquist Patent 1,770,422, July 15, 1930. With this arrangement wherein the phase change introduced by the line is corrected the phase angle meter always directly indicates the phase angle between voltages V1 and V2. The general description of Fig. 4 is obviously applicable to this figure.

Fig. 6 shows another application of this invention wherein it is employed for measuring the phase angle difference between two different power systems or two different points on the same power system. The two different power systems A and B or the two different points on the same power system are connected through suitable coupling means by a pilot circuit for comparing the phase relationship of the two systems or points on the same system. The power systems, or system, are shown as three-phase systems and the pilot circuit Hill is connected at two selected points A and B by means of suitable coupling elements across one phase of the power line. Measuring the phase difference between the two points in one phase of a polyphase system may be sufficient when the several phases are substantially balanced, but if phase angle measurements for the other phases of a polyphase system are desired, they may be made for the other phases of the power system'either by employing a pilot circuit for each phase or by having switching devices for synchronously switching the pilot circuit connections from one phase to another of the power system. The arrangement here shown is similar to that of Fig. 5 for measuring the phase angle between two sources of voltage and is here applied to measure the phase angle between the two points on one phase of the power system or systems A and B, irrespective of the location of the source or sources of power. The series resistances R1 and R2 must be high in comparison with the terminating impedance Zr at each end of the pilot circuit. The phase compensator 300 compensates for any phase displacement caused by the pilot circuit and consequently the readings of the phase angle meter 200 show directly the phase difference between the voltages of the diiferent power systems.

Fig. 7 shows a further application of this invention as applied to power transmission for automatically maintaining two different power systems or two different points in the same power system in phase. The arrangement here shown is similar to that of Fig. 6 but employs in addition automatic means for adjusting the phase relationship of one system to that of another system so that they may be automatically maintained substantially in phase with one another. A different relay arrangement 400 is here substituted for the phase angle meter measuring arrangement shown in Fig. 6 which automatically operates when there is a difference in phase between the two systems A and B. When a relative phase change occurs in one direction, the relay closes a circuit which operates an adjusting mechanism 500 connected with local control apparatus to cause a shift in the proper direction of the phase in the local system, and when the relative phase change is in the opposite direction, the relay closes another circuit which causes a shift in the opposite direction of the phase of the local system, thereby automatically causing a phase change in the local system to substantially eliminate the phase difference between the systems. The differential relay arrangement 400, as here shown, consists of two vacuum tubes dill and 402 in push-pull arrangement and so connected that the output circuit of each tube controls the energization of one side of a differential relay 0 which in turn operates the phase adjusting mechanism 500, and thus maintains a balance in the phase relationship of the systems. The input circuits of this differential relay arrangement are connected by suitable coupling transformers with the pilot circuit I00 interconnecting the power systems A and B and with a local circuit associated with the power system B. The adjusting mechanism 500 which may be mechanically connected to the local control apparatus for adjusting the phase relationship of the local system to that of the other system may be of any suitable type such as is now used and mechanically operated for changing the phase relationship of a power system with that of another such system. Fig. 7, as above stated, relates primarily to the automatic control of the relationship rather than to the mechanism operating the local control apparatus. The adjusting mechanism may be of any suitable type such, for example, as that shown in Patent 1,703,142 to E. I. Green, especially Fig. 2a in which relay 32 may correspond to relay 4 l 0 of the present application.

All of these applications are made practicable by providing a circuit of substantially constant phase relation.

This invention may be applied to any line, within the limits outlined above, for which the phase characteristic is required to be substantially constant.

While this invention has been disclosed as embodied in certain particular forms, it is to be understood that it is not limited to such forms but is capable of embodiment in other forms without departing from the spirit and scope of the appended claims.

What is claimed is:

1. In combination with an electrical system, means for measuring the phase difference of the voltages at two points on said system, which consists of a pilot circuit between the two said points,

means for compensating for variations in phase displacement in said pilot circuit by terminating both ends with equal impedances having large values compared with one-half the series impedance of the equivalent T-network of said pilot circuit, coupling means for impressing the voltage at one of said points upon said pilot circuit, and means associated with said pilot circuit for measuring the phase angle between said voltages.

2. In combination with a power system, means for measuring the phase difierence of the voltages at two points on said system, which consists of a pilot circuit between the two said points, said pilot circuit being terminated at both ends with equal impedances having large values in comparison with one-half the series impedance of the equivalent T-network of said circuit, coupling means for impressing the voltage at one of said points of said power system upon said pilot circuit, and means at the other end of said pilot circuit for measuring the phase angle between the voltage at the other of said points on said power system and that impressed on said pilot circuit.

3. In combination with a power system, means for measuring the phase difference of the voltages at two points on said system, which consists 01' a pilot circuit between the two said points, said pilot line being terminated at both ends with equal impedances having large values in comparison with one-half the series impedance of the equivalent T-network of said circuit, coupling means for impressing the voltage at one end of said points of said power system upon said pilot circuit, means for compensating for phase displacement in said pilot line, and means at the other of said points of said power system for measuring the phase angle between the voltage at the said other point on said power system and that impressed on said pilot circuit.'

4. In combination with a power system, means for comparing the phase difference of the voltages at different points on said system, which consists of a pilot line between said points, said pilot line being terminated at both ends with equal impedances having a value large in comparison with one-half the series impedance of the equivalent T-network of said circuit, coupling means for impressing the voltage at one of said points upon said pilot line, means for compensating for phase displacement in the said pilot line, means including said pilot line connecting between the said points of said system for comparing the phase angle between said voltages, and means controlled by said comparing means for automatically adjusting the phase relationship 01' said voltages so that the phase angle between said voltages is substantially nil.

5. In combination with a power system, means for comparing the phase difference of the voltages at diflerent points on said system, which consists of a pilot line between the said points, said pilot line being terminated at both ends with equal impedance having the value large in comparison with one-half the series impedance of the equivalent T-network of said circuit, coupling means for impressing the voltages at one of the said points upon said pilot line, means for compensating for phase displacement in the said pilot line, means including said pilot line connecting between said points of said system for comparing the phase angle between said voltages, and means controlled by said comparing means for automatically adjusting the load at the two points in said power system in accordance with the phase angle between the said voltages.

6. In combination with a polyphase power system, means for measuring the phase difference of the voltages at two points on said system which consists of a pilot line between the said points, coupling means for impressing the voltage of the power circuit at two 0! said points upon said pilot line, means for compensating for variations in phase displacement in the said pilot line, and means including the said pilot line on said system for controlling the phase angle between said voltages at each of said points of said power system.

NEWTON MONK. 

